The present invention relates generally to grapple equipment for manipulating tree length logs and more particularly to a grapple attachment for the end of a boom on a vehicle.
Log grappling devices are well known in the lumber and logging industry. These devices are used for removing logs from the forest area where they have been cut, moving them from one place to another, stacking, and loading and unloading them from trucks and railroad cars. One type of grappling device that has been in existence for numerous years consists of a grapple assembly pivoted on the outer end of a boom with a heel fixed to the grapple assembly and a pair of co-operable jaws pivoted on the assembly to grip the log. This type of device is shown in Larson U.S. Pat. No. 3,165,215 and Tanguay U.S. Pat. No. 3,709,390.
One of the problems encountered with this type of grappling device is the fact that the boom supporting the grapple assembly must be in general longitudinal alignment with the log to be picked up so that the log can be grasped by the grapple arms and stabilized by the grapple heel. Usually, when operating in a forest, the logs are of full length, being the height of the tree, which is substantially greater than the overall length of the grapple assembly and even the boom assembly supporting the grapple assembly. Thus, it is customary when utilizing grapple assemblies of the above type, to grasp the tree length log adjacent the base end, which is substantially greater than the opposite end so that the smaller end is cantilevered beyond the end of the grapple assembly. It should be noted that in devices of the above type, the heel is located inwardly of the position of the grapple jaws with respect to the boom upon which it is supported.
One of the problems encountered in utilizing such devices, particularly when the tree length logs are to be stacked on trucks or railroad cars, is the fact that the logs cannot be positioned on the trucks or railroad cars to fully utilize the space on the vehicle in a most efficient manner. As indicated above, tree length logs generally are substantially greater in diameter adjacent the butt or base end than they are adjacent the opposite end. With grapple assemblies of the above type, it is mandatory that the butt or base end of the tree be grasped which means that all of the trees must be inserted on the vehicle with the butt ends in abutting relation to each other. This means that a substantial area, particularly adjacent the tip ends of the tree is wasted in the transportation of logs from one site to another.
In order to alleviate this problem, it has recently been proposed to support the grapple assembly for universal pivotal rotation about a generally vertical pivot axis on the outer end of the boom. This type of device is disclosed in Jones et al. U.S. Pat. No. 3,631,995 and consists of a lower grapple head that is rotatably supported on an upper grapple head pivoted on the outer end of a boom. The lower grapple head has two pivotally supported grapple heels which engage the tree at selected locations as well as a pair of grapple arms for grasping the tree. While this type of unit has found some degree of commerical success, there are inherent shortcomings in a unit of this type, particularly the overall cost thereof.
The unit of the type disclosed in the above-mentioned Jones et al. patent requires four separate cylinders on the lower head of the grapple assembly, which of necessity requires very complicated hydraulic circuitry between the vehicle which supports the boom and the grapple assembly supported on the outer end of the boom.